As having excellent melt moldability, secondary
processability, mechanical characteristics and economical efficiency, hydrophobic thermoplastic resins such as polyolefins and polystyrenes are widely used for various applications. For example, in the field of food packaging industry, they are used for producing films and containers such as bottles, cups, etc.; while in the field of non-food industry, they are used in various daily necessities, parts of electric or electronic appliances for household use, car parts, etc. Multi-layered structures comprising hydrophobic thermoplastic resin and ethylene-vinyl alcohol copolymer (hereinafter referred to as EVOH) are widely used in the field of food industry or the like that requires barrier properties to oxygen, flavors, etc.
Laminating hydrophobic thermoplastic resin and EVOH makes it possible to produce laminate structures having the characteristics of the two. Apart from this, techniques of blending the two are also widely employed in various fields.
However, EVOH is a resin having high hydrophilicity, and its compatibility with hydrophobic thermoplastic resins is poor. Therefore, combining EVOH with hydrophobic thermoplastic resin is often problematic in that resin compositions having good physical properties could not be obtained. Various types of compatibilizers for the two, such as typically polyolefinic resins having polar functional groups have heretofore been studied, but their effects are not always satisfactory. In that situation, it is desired to develop more effective compatibilizers capable of satisfactorily compatibilizing the two.
The technique of laminating hydrophobic thermoplastic resin such polyolefin or polystyrene with EVOH is useful, but is often problematic in producing complicated or small-sized laminates, since it is difficult to produce them through multi-layered lamination using the two. In that situation, it is desired to develop thermoplastic resins capable of being formed into single-layered barrier structures. Japanese Patent Application Laid-Open (JP-A) Hei-6-80150 (European Patent 584,808) discloses one example of a single-layered barrier structure, in which is used a resin composition comprising three components of polyolefin, EVOH having a melting point of not lower than 135.degree. C. and EVOH having a melting point of 130.degree. C. or lower, for producing the head of a two-piece tube container composed of a head and a cylindrical body. However, the head disclosed therein is not still satisfactory, as its characteristics including barrier properties, mechanical strength and adhesion strength to cylindrical bodies are not always good.
Hydrophobic thermoplastic resins such as polyolefins, polystyrenes and the like have various drawbacks owing to their hydrophobic properties. For example, when articles of those resins are painted, the adhesion strength between their surfaces and paint vehicles (that is, the coatability of their surfaces with paint vehicles) is poor since the surfaces have non-polar properties. One drawback of the resins is that the resin articles must be subjected to primer treatment prior to coating in order to improve the coatability of their surfaces, thereby resulting in that the coating costs are high. Recently, organic solvent-based paints are being replaced by aqueous paints for the protection of the environment. However, the compatibility of aqueous paints with hydrophobic thermoplastic resins is extremely low. In that situation, it is much more desired to develop thermoplastic resins with improved coatability.
On the other hand, EVOH is known to be useful in the field of food industry that requires barrier properties to oxygen, odors, flavors or the like, for example, as wrapping or packaging films for foods, etc.
At present, however, EVOH is used little by itself, as its toughness is poor. For example, one drawback of EVOH films is that they often have pin holes when repeatedly folded or deformed.
In order to overcome its poor toughness and flexibility, EVOH is often formed into multi-layered structures by laminating layers of EVOH and thermoplastic resin such as polyethylene, polypropylene, polyamide or the like, along with layers of adhesive resin. However, as so mentioned hereinabove, it is often difficult to produce complicated or small-sized, multi-layered structures of thermoplastic resin and EVOH. Therefore, EVOH is often used by itself to form single-layered structures for complicated or small-sized articles. Even if multi-layered structures composed of EVOH and thermoplastic resin layers are formed, their applications are often limited since their properties are not good because of the poor flexibility of the EVOH resin layer. Accordingly, it is desired to develop a resin composition comprising EVOH, which has good flexibility while still getting the barrier properties intrinsic to EVOH.
In order to overcome the drawbacks of EVOH, various methods have heretofore been reported for combining EVOH with ethylenic polymers having good flexibility. However, most of them are still unsatisfactory in that the flexibility and drawability of the resin compositions produced therein is still poor and that the transparency intrinsic to EVOH is greatly lowered in the resin compositions. At present, therefore, the reported methods have few practical applications in the art. In that situation, it is desired to develop a resin composition having excellent flexibility, drawability and transparency.
EVOH has excellent chemical resistance, oil resistance, stain resistance and plasticizer shieldability, and EVOH films are much used in interior finish work. For example, an EVOH film is laminated on the surface of interior material such as wallpaper, decorative plywood, polyvinyl chloride leatherette, etc. However, EVOH films have a high degree of surface gloss, and are therefore problematic in applications for wallpaper, leatherette and the like that must be matted. In those applications, EVOH films shall be matted by applying thereto matting rolls under heat and pressure. However, if sufficient pressure could not be applied thereto, EVOH films could not be well matted. Apart from the method of using matting rolls for matting films, known are (1) a sand-blasting method, (2) a surface-treating method with chemicals, and (3) a method of adding powdery inorganic substances. However, all those methods are defective in that they are expensive and their producibility to form films is poor. In particular, the method (3) of adding powdery inorganic substances is not suitable for EVOH. This is because, if a large amount of a powdery inorganic substance is added to EVOH so as to attain the intended matting result, the resulting EVOH films will have pin holes and will not able to produce films.
One method of solving this problem is disclosed in JP-A Sho-64-74252, which provides a mat film comprising from 50 to 95% by weight of EVOH and from 5 to 50% by weight of a carboxylic acid-modified polyethylene resin and in which at least one surface of the mat film provided has a degree of surface gloss of not higher than 60%. However, the blend resin composition used therein is still unsatisfactory as its thermal stability is poor.
Where multi-layered containers (bottles, cups, etc.) comprising a thermoplastic resin and an EVOH resin are produced, the process gives scrap (burs in producing bottles, blanked-off scrap in producing cups, etc.). To recycle the scrap, generally employed is a method of interposing a scrap-recycled layer between a thermoplastic resin layer and an EVOH layer of multi-layered containers. In that method, however, where the recycled mixture comprising a thermoplastic resin and an EVOH resin is melt-extruded to form the scrap-recycled layer, its flow stability is often disordered because of the poor compatibility between the EVOH resin and the thermoplastic resin and of the thermal deterioration of the EVOH resin, often resulting in that the multi-layered sheets having the scrap-recycled layer and the moldings formed from them through thermoforming will have wavy patterns on their surfaces.
In order to solve this problem, a method has been proposed of adding, as a compatibilizer, an EVOH having an ethylene content of from 68 to 98 mol % and a degree of saponification of the vinyl acetate component of at least 20%, to a mixture of an EVOH having an ethylene content of from 20 to 65 mol % and a degree of saponification of the vinyl acetate component of at least 96% and a thermoplastic resin (see JP-A Hei-3-215032, U.S. Pat. 5,094,921). However, the proposed method is not so much effective enough to completely remove the wavy patterns of the multi-layered sheets and their moldings. Therefore, it is desired to develop more powerful compatibilizers.
JP-A Hei-4-164941 discloses a polyolefinic resin composition having excellent barrier properties, which comprises from 50 to 99.5% by weight of a polyolefin, from 0.4 to 50% by weight of an EVOH, and from 0.1 to 15% by weight of a graft polymer having been prepared by grafting a polyolefin with an ethylenic unsaturated carboxylic acid or its derivative followed by melt-mixing it with apolyamide. JP-AHei-4-164944 discloses an EVOH-based resin composition having excellent waterproofness, excellent gas barrier properties in high-humidity atmospheres, and excellent drawability and flexibility, which comprises from 0.4 to 50% by weight of a polyolefin, from 50 to 99.5% by weight of an EVOH, and from 0.1 to 15% by weight of the graft polymer noted above.
In those, however, the modified polyolefin to be melt-mixed with a polyamide is one as prepared by grafting a polyolefin with an unsaturated carboxylic acid or its derivative, and this is not a random copolymer. Being different from those techniques disclosed, the present invention uses a random copolymer. As will be demonstrated in Comparative Examples to be mentioned hereinunder, using graft copolymers could not attain the object of the present invention.
JP-A Hei-8-217934 (European Patent Laid-Open No. 797,625) discloses a thermoplastic resin composition comprising from 50 to 85 parts by weight of an EVOH, from 10 to 40 parts by weight of an ionomer of an ethylene-unsaturated carboxylic acid copolymer having an unsaturated carboxylic acid content of from 4 to 15 mol %, and from 1 to 25 parts by weight of a polyamide. They say that the composition disclosed has excellent gas barrier properties, impact resistance, pin-hole resistance, ductility, drawability and transparency. JP-A Hei-9-77945 (European Patent Laid-Open No. 797,625) discloses a resin composition as prepared by adding from 0.01 to 3 parts by weight of a metal salt of a fatty acid to 100 parts of the resin composition of JP-A Hei-8-217934. They say that the resin composition disclosed has better thermal stability.
However, as will be demonstrated in Comparative Examples to be mentioned hereinunder, the flexibility, especially the bending resistance of those resin compositions disclosed is still unsatisfactory even though they comprise an EVOH as the major component. Nothing is referred to in those prior publications relating to a technique of adding a specific hydrophobic thermoplastic resin to the resin compositions comprising the three components noted above.
Japanese Patent Publication (JP-B) Sho-51-41657 (USP 3,857,754 and 3,975,463) discloses a resin composition having excellent processability and gas barrier properties, which comprises from 30 to 98 parts by weight of a low-density polyethylene, from 2 to 70 parts by weight of an EVOH, and from 0.5 to 15 parts by weight of at least one thermoplastic polymer having a carbonyl group in its main chain or side chain and selected from ionomers and polyamides. They say that both an ionomer and a polyamide may be in the composition but are silent at all about the fact that adding the combination of the two to the composition is preferred and about the effect of the two added in combination. In addition, nothing is referred to in the publication relating to the mixing ratio of the polyamide and the ionomer to be combined.
In this connection, we, the present inventors have verified that the absence of any one of a polyamide or an ionomer could not attain the object of the present invention, as in Comparative Examples to be mentioned hereinunder.
In that background noted above, one object of the present invention is to provide a resin composition having excellent compatibility while having excellent barrier properties, mechanical strength, flexibility, drawability, melt stability, heat sealability, coatability, stain resistance and transparency. Another object of the invention is to provide a resin composition comprising a thermoplastic resin and an EVOH for multi-layered structures, of which the scrap is well recycled in producing moldings without making the moldings have wavy patterns on their surfaces.
The wording of barrier properties as referred to herein is not limited to only the concept of so-called gas barrier properties to gases such as oxygen, nitrogen, carbon dioxide and the like, but shall include any other concepts of non-adsorbability and non-perviousness to flavor components (e.g., limonene, etc.), odor components (e.g., skatole, etc.) and hydrocarbons such as gasoline, etc.